Vacuum may be used to operate or to assist in the operation of various devices of a vehicle. For example, vacuum may be used to assist a driver applying vehicle brakes. In some vehicle systems vacuum is provided via a vacuum pump. Some vacuum pumps are electrically driven by motors while others are mechanically driven by the vehicle's engine. Engine driven vacuum pumps can operate at higher efficiencies than electrically driven vacuum pumps; however, operation of mechanically driven vacuum pumps is constrained by engine operation. For example, mechanically driven vacuum pumps do not pump air while the engine is not rotating. On the other hand, electrically driven vacuum pumps may be activated and deactivated without regard to engine operation so that engine fuel economy can be increased; however, electrically driven vacuum pumps can be less efficient than mechanically driven vacuum pumps. Thus, opportunities exist to improve on the operation of both electrically and mechanically driven vacuum pumps.
The inventor herein has recognized the above-mentioned disadvantages and has developed an engine vacuum system, comprising: an engine; an electrically driven vacuum pump in fluid communication with the engine and a vacuum reservoir, a vacuum pump exhaust port of the electrically driven vacuum pump in fluid communication with an interior region of a crankcase or cylinder head valve cover of the engine.
By directing the outlet of an electrically driven vacuum pump to an area interior to an engine, it is possible to use engine oil lubricate the mechanism and to wet the pumping chamber seals of an electrically driven pump so that the pump has higher pumping efficiency without increasing vehicle emissions. For example, air can be pumped on demand from a vacuum reservoir by an electrically driven vacuum pump to an engine crankcase. Oil used to wet seals of the vacuum pump can be deposited into the engine crankcase, and air from the vacuum reservoir can be routed to engine cylinders via a positive crankcase ventilation (PCV) system for participation in combustion of an air-fuel mixture. In this way, the pumping efficiency of the electrically driven vacuum pump can be increased without increasing engine emissions. In other examples, air exhausted from an engine driven vacuum pump with an oil wetted pumping chamber can be routed to a region of the engine enclosed by a cylinder head valve cover to reduce vehicle emissions. The valve covers enclose the valve train and limit the flow of oil and other substances to atmosphere.
The present description may provide several advantages. In particular, the approach can improve the operation of electrically and engine (mechanically) driven vacuum pumps that have oil wetted seals. Further, the approach can reduce vehicle emissions for vehicles that have vacuum pumps. Further still, the approach may provide improved vacuum pump control during some conditions.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.